Mediacenter network advice

Thinking of purchasing an Xbox, Ps3 or similar to connect to my LCD tv. But not sure where to start

I want to be able to setup a network with my other pc's in the house. Main usage will be playing movies (xvid, divx, dvd), playing music and surfing the net. Gamings not that important. Meaning we want a cheap box with good tv out quality, network support, HDD support, USBs support. Preferably a box who don't need much tinkering to setup. And if possible a box who support other OS installations (Ubuntu desktop edition, Mythbuntu, Media portal or likewise).

Can people give some advice as to what have worked for them and how? What's your specs, how did you set up the network, what OS(s) are you running, how is tv out quality? And if people have links to sites dealing with things like this please post them as well.